[invincing]

This is not about peak sensitivities. The RGB colors are used as primaries because they provide a large response on one type of cones, and as small as possible response on the two other types of cones.

Blue is chosen to have as small wavelength as possible (S=small) and red is chosen to have as long wavelength as possible (L=long), while both being still in the visible spectrum with large enough response from S and L cones respectively.

Since M and L response profiles overlap anyway and just the ratio of the response changes, green is chosen to be as far away from the red, but still outside of the response curve of S cones that get stimulated by blue. This happens to be also around the peak sensitivity for the M cones.